Research ArticleChemistry

Tip-enhanced ablation and ionization mass spectrometry for nanoscale chemical analysis

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Science Advances  08 Dec 2017:
Vol. 3, no. 12, eaaq1059
DOI: 10.1126/sciadv.aaq1059
  • Fig. 1 Schematic diagram of the TEAI-TOFMS system and spectra of Ti using fs-laser–induced TEAI.

    (A) Experimental setup. (B) Enlarged view of the ion source. (C) Enhancement factor of electromagnetic power density of near-field enhancement by a shell-isolated apertureless tip. (D) Scanning electron microscopy (SEM) images after performing 200 pulses of fs-laser in the retracted mode. (E) SEM images after performing 200 pulses of fs-laser in the approached mode. (F) Spectra corresponding to the modes used in (D). (G) Spectra corresponding to the modes used in (E). (H) SEM image of the array fs-laser TEAI obtained after performing 200 pulses at each spot. (I) Corresponding mass spectra of (H).

  • Fig. 2 Study of crater formation on the surface of Au@Ti and corresponding MS spectra.

    (A) SEM images in the retracted mode after 1600 laser pulses were applied. (B to H) SEM images in the approached mode after 40 to 1600 laser pulses were applied. (I) Relevant spectra obtained at the same condition for (A) to (H).

  • Fig. 3 Comparative study of TEAI-TOFMS and SIMS to analyze a residue mixture of nine inorganic salts.

    (A) Image of the residue deposited on a Cu substrate. (B) SEM image of the residue deposited on a Cu substrate. (C) SEM image of the center area of the coffee ring, where the surface was smoothed by ethanol. (D) TEAI-MS spectrum in the approached mode by sampling 10 spots with 400 laser pulses per spot. (E) Enlarged spectrum of (D); the inset is the spectrum in the retracted mode. (F) SIMS spectrum of the residue obtained from 200 scans (128 × 128 spots per scan, 1 shot per spot). (G) Enlarged spectrum of (F).

  • Fig. 4 Results of MSI with a lateral resolution of 50 nm.

    (A) SEM image of the KI residue on a Si substrate coated with a 10-nm layer of Au. The area inside the red square represents the area of interest. (B) Image of 39K+ distribution obtained by fs-laser–induced near-field MSI with a lateral resolution of 50 nm by scanning an array of 20 × 20 spots at 50-nm spot intervals with 40 shots per spot. The color scale shows the normalized intensity of 39K+. (C) Typical mass spectrum in an MSI experiment.

  • Fig. 5 FDTD-simulated distribution of Poynting vector.

    (A) Magnitude of Poynting vector in the vertical XZ panel (Y = 0 nm). (B) Magnitude of Poynting vector in the horizontal XY panel (Z = 0 nm).

  • Fig. 6 Simulation results of tip-enhanced ablation, plasma initiation, expansion, and ionization processes.

    (A) 3D bulk temperature (at 3000 fs) from one shot. (B) Final ablation crater by one shot. (C) Plasma temperature from one fs-laser shot at 3000 fs. (D) Total/ionized particle number density from one shot at 3000 fs.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/12/eaaq1059/DC1

    table S1. Operating parameters of the TEAI source.

    table S2. Experimental and theoretical ablated Ti particle numbers with 40 laser shots.

    fig. S1. Images of the shell-isolated tip.

    fig. S2. Picture of Au (111) with a 10-nm layer of Ti taken by a metallurgical microscope.

    fig. S3. Preparation progress of the micropatterned KI sample.

    fig. S4. AFM images of the surface of Au@Ti.

    fig. S5. SEM images of the area of interest.

    fig. S6. Demonstration of lateral resolution analysis.

    fig. S7. Morphologic comparison of tips used in TEAI experiment.

  • Supplementary Materials

    This PDF file includes:

    • table S1. Operating parameters of the TEAI source.
    • table S2. Experimental and theoretical ablated Ti particle numbers with 40 laser shots.
    • fig. S1. Images of the shell-isolated tip.
    • fig. S2. Picture of Au (111) with a 10-nm layer of Ti taken by a metallurgical microscope.
    • fig. S3. Preparation progress of the micropatterned KI sample.
    • fig. S4. AFM images of the surface of Au@Ti.
    • fig. S5. SEM images of the area of interest.
    • fig. S6. Demonstration of lateral resolution analysis.
    • fig. S7. Morphologic comparison of tips used in TEAI experiment.

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